The invention relates in particular to a heart assist system, also called a heart pump for short. In the prior art, a heart pump is used so that a heart that has become too weak is helped to pump blood. For this purpose, the heart pump is implanted in the body of the patient and is connected to the aorta and to the heart via blood-conveying tubes. The heart pump contains an impeller, which induces a strengthening of the blood flow. The impeller is driven by an electric motor. A control unit carried around outside the body, and batteries for supplying energy, are connected to the heart pump via a power cable that leads through the skin of the patient. The control unit and the batteries can be carried around by the patient on a belt or on shoulder straps. The impeller of the heart pump can be connected to the motor shaft. Various materials are used in the prior art to support the motor shaft and therefore the impeller, said materials each bringing with them specific disadvantages.
In the prior art, for example, ceramics are used as materials of a sliding bearing. Such ceramics have a low thermal conductivity. In the sliding bearing of the heart pump, this can lead to local heating and, consequently, to increased wear. Moreover, local heating of this kind can lead to clotting of the patient's blood. This can cause the death of the patient. Moreover, in the prior art, metals are used as materials for sliding bearings in heart pumps. However, metals have rather poor wear resistance. Moreover, in the prior art, coated sliding-bearing components are used in heart pumps. When using coated components, in particular in a mechanical bearing, there is always a residual risk of the coating peeling off. Coating parts which have peeled off, and which are released into the patient's body, may likewise lead to the death of the patient. Moreover, the prior art discloses the use of stones such as ruby as a bearing material. These have poor thermal conductivity, and therefore the comments made regarding the local heating of ceramics also apply here. Graphite, which is likewise known in the prior art as a bearing material, has low hardness and, consequently, is subject to considerable wear. The same applies to plastics as bearing materials. Sintered sliding bearings are also known in the prior art. During use, sintered and often porous sliding bearings in most cases result in mixed friction, since liquid can settle in the pores of the sintered material and thus serves as lubricant. If such a bearing is used in a heart pump, the liquid is blood. If blood settles in the pores, it can form clumps and cause growth of tissue around the bearing material, which can have a disadvantageous effect on the function of the heart pump and on the patient. Moreover, in the prior art, magnetic bearings with permanent magnets (DE 11 2006 002 413 T5) or combined magnetic/mechanical bearings (WO 98/00185A1, DE 196 25 300 A1) are also used in heart pumps. Such magnetic bearings have relatively low wear but are very elaborate to produce. Moreover, the magnetic field of the permanent magnets of the bearing can have a negative impact on other electromagnetic devices. Moreover, the precisely set magnetic field of the bearing can be disturbed by external electromagnetic fields, which can lead to misalignment of the magnetic bearing.
It is generally an object of the present invention to at least partially overcome a disadvantage arising from the prior art. It is an object of the invention to make available a heart pump which, when implanted in a patient, can lead to reduced clot formation during its operation. It is a further object of the invention to make available a mechanical bearing which is characterised by an as far as possible advantageous combination of low friction, high wear resistance and high thermal conductivity. It is a further object of the invention to make available a mechanical bearing which is as far as possible made only of biocompatible materials. It is a further object of the invention to make available a mechanical bearing which as far as possible contains no coating of the bearing components. It is a further object of the invention to make available a mechanical bearing which is characterised by a combination of the aforementioned features. It is a further object of the invention to make available an implantable medical appliance, for example a heart pump or a blood pump or both, with a mechanical bearing which achieves one of the aforementioned objects. Here, an actuator or an impeller is preferably supported in a movable manner by the mechanical bearing.
A contribution to the at least partial achievement of at least one of the above objects is made by the independent claims. The dependent claims set forth preferred embodiments that contribute to the at least partial achievement of at least one of the objects.